Project Summary

Baleen whales (mysticetes) are an extant group of cetaceans (whales and dolphins) and have a long and rich fossil record, and fossils of extinct baleen whales have proven invaluable for reconstructing the timing and sequence of anatomical changes leading up to modern lineages. The earliest baleen whales primitively retained teeth, and although transitional toothed mysticetes have been reported with bony correlates of baleen – providing an anatomical transition between tooth-bearing and baleen-bearing mysticetes – other changes in skull anatomy and the particular changes in feeding ecology occurring within this transition remain poorly known. The Eomysticetidae are a recently recognized group of early-diverging toothless baleen whales, thus far only reported from South Carolina, USA. Eomysticetids are relatively large (~10 meters body length) with hyper-elongate and flattened snouts, ‘grooves’ in the palate suggesting the presence of baleen, large areas for jaw muscle attachment, small eye sockets, and long, delicate mandibles. The extreme proportions of their feeding apparatus are distinctive in comparison to all previous and subsequent baleen whales (tooth- or baleen-bearing).

The discovery of a large volume of eomysticetid fossils, including multiple anatomically informative skulls with associated mandibles, earbones, and postcranial skeletons from the Oligocene Kokamu Greensand and Otekaike Limestone of north Otago and south Canterbury, and the reinterpretation of “Mauicetus” lophocephalus and “Mauicetus” waitakiensis (Marples, 1956) as eomysticetids suggests an unexpected diversity of these archaic mysticetes. This dissertation study proposes to 1) describe the skeletal anatomy of these new eomysticetid taxa in order to further clarify our anatomical knowledge of the family, 2) carefully redescribe fossils of “Mauicetus” originally named by Marples; 3) place these taxa within a phylogenetic context and test hypotheses of eomysticetid monophyly (or alternatively, paraphyly), and 4) investigate the possible implications of the eomysticetid “archetype” for the evolution of the feeding apparatus in early baleen whales.

Fellow Ph.D. student Cheng-Hsiu Tsai prospecting for fossil cetaceans in the Otekaike Limestone in North Otago, March 2012.

Research Collaborations

I have a number of other studies I am currently collaborating on with other colleagues. Several of these are with colleague Morgan Churchill (University of Wyoming, USA) regarding the fossil record and phylogeny of pinnipeds: two studies are nearing completion, focused on description of new fossil material of the rare walrus Pelagiarctos and reevaluating previous interpretations of its ecology as a “Killer walrus”, and a combined phylogenetic analysis of the Otariidae (fur seals and sea lions) based on a combination of molecular data and a new, large morphological data set.

Description of newly collected and anatomically informative crania, earbones, and mandibles of the bizarre dwarf baleen whale Herpetocetus bramblei and a two new species of Herpetocetus from the late Neogene of California (Purisima and San Diego Formations) involves collaborative study with Jonathan Geisler (NYCOM, Anatomy Dept., USA) and Joe El Adli (San Diego Natural History Museum, USA). These studies are concerned with the morphology, feeding ecology, ontogeny, and phylogenetic relationships of these strange cetaceans.

The preservation of modern and fossil vertebrates within the marine environment is poorly understood, and collaboration with Laura Vietti (University of Minnesota, USA) and Nick Higgs (University of Leeds, UK) is arranged for assembling a comprehensive review and perspective on processes affecting vertebrate skeletons in the marine realm. Higg’s and Vietti’s actualistic taphonomic backgrounds will greatly complement my “historical” perspective.

Fossil birds have a surprisingly extensive Neogene fossil record in marine strata, and ongoing collaboration with N. Adam Smith (NESCENT, North Carolina, USA) will attempt to describe and analyze the avifauna of various marine formations in Northern California. This resulted in one publication (Boessenecker and Smith, 2011) documenting a geologically young bony toothed bird from California.

Robert W. Boessenecker prospecting for fossil sea lions in the Pleistocene Port Orford Formation of southwestern Oregon, March 2009

Previous research and the Purisima Formation vertebrate assemblage

Owing to a field-based study in 2005-2006 of a newly discovered fossil vertebrate locality in the Pliocene Purisima Formation of Northern California, early on my research interests became focused on fossil marine mammals. Extensive paleontological field work in the Purisima Formation added a large volume of vertebrate fossils (sharks, bony fish, birds, pinnipeds, and cetaceans), and a long term research goal is to publish and describe many of these new finds, including new species of pinnipeds and cetaceans. Several published studies have resulted from this so far, papers describing a pilot whale-like odontocete and an entire marine mammal fossil assemblage are currently underway.

Because the Purisima Formation preserves fossil vertebrates in a number of depositional settings (offshore, transitional zone, shoreface), it offers a unique opportunity to study onshore-offshore changes in vertebrate preservation. Previous studies of marine vertebrate taphonomy have focused on individual skeletons, localities, or formations, and thus far have not attempted to examine onshore-offshore trends. My master’s thesis focused on the comparative taphonomy of these marine vertebrate assemblages, and documented onshore-offshore changes in preservation and a strong link between preservation and sequence architecture, indicating a strong relationship between fossil preservation and physical depositional processes.

Robert W. Boessenecker and Richard Hilton (Sierra College, Rocklin, California) collecting fossil cetaceans and walruses during a canoe expedition in Northern California; a 200 lb sandstone block containing a complete walrus skull was successfully removed from a remote area with the use of a canoe and cargo net. September, 2011.

El Adli, J., Deméré, T.A., and Boessenecker, R.W. In press. A new species of the diminutive baleen whale Herpetocetus (Cetacea: Mysticeti) from the upper Pliocene (Piacenzian) of California, USA with observations on the evolution and relationships of the Cetotheriidae. Zoological Journal of the Linnean Society.

Boessenecker, R.W. 2013. A new marine vertebrate assemblage from the Late Neogene Purisima Formation in Central California, Part II: Pinnipeds and Cetaceans. Geodiversitas 35:4:815-940. doi:10.5252/g2013n4a5

Boessenecker, R.W. and M. Churchill. 2013. A reevaluation of the morphology, paleoecology, and phylogenetic relationships of the enigmatic walrus Pelagiarctos. PLoS One 8(1) e54311. doi:10.1371/journal.pone.0054311

Boessenecker, R.W. 2011C. A new marine vertebrate assemblage from the Purisima Formation in Central California, Part 1: fossil sharks, bony fish, birds, and implications for the age of the Neogene Purisima Formation west of the San Gregorio fault. PalArch's Journal of Vertebrate Paleontology 8(4):1-30. Purisima publication (Palarch)

Conference Presentations

El Adli, J., and R.W. Boessenecker. 2011. The musculature of the temporomandibular region in the Mio-Pliocene baleen [whale] genus Herpetocetus and its inference for feeding strategy. Journal of Vertebrate Paleontology 31:104A.

Boessenecker, R.W. 2011. Marine vertebrate taphofacies of the Neogene Purisima Formation of central California: implications for the study of fossil marine vertebrates and their depositional context. Sixth Triennial Conference on Secondary Adaptation of Tetrapods to Life in Water Program with Abstracts: 12.

Churchill, M.M., Boessenecker, R.W., and M.T. Clementz. 2011. Conservation implications of a new phylogeny of fur seals and sea lions. Annual meeting of the Society for Marine Mammals.

Churchill, M.M., Boessenecker, R.W., and M.T. Clementz. 2011. The systematics of Otariidae, and the influence of allometry and polymorphism on morphology based phylogenetics. Sixth Triennial Conference on Secondary Adaptation of Tetrapods to Life in Water Program with Abstracts: 17.

El Adli, J., Boessenecker, R.W., and J. H. Geisler. 2011. Taxonomic problems of and relationships among species of the fossil baleen whale genus Herpetocetus. Sixth Triennial Conference on Secondary Adaptation of Tetrapods to Life in Water Program with Abstracts: 23.